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1.  Bacteria that glide with helical tracks 
Current biology : CB  2014;24(4):R169-R173.
Many bacteria glide smoothly on surfaces, but with no discernable propulsive organelles on their surface. Recent experiments with Myxococcus xanthus and Flavobacterium johnsoniae show that both distantly related bacterial species glide utilizing proteins that move in helical tracks, albeit with significantly different motility mechanisms. Both species utilize proton motive force for movement. However, the motors that power gliding in M. xanthus have been identified, while the F. johnsoniae motors remain to be discovered.
doi:10.1016/j.cub.2013.12.034
PMCID: PMC3964879  PMID: 24556443
2.  The lethal cargo of Myxococcus xanthus outer membrane vesicles 
Myxococcus xanthus is a bacterial micro-predator known for hunting other microbes in a wolf pack-like manner. Outer membrane vesicles (OMVs) are produced in large quantities by M. xanthus and have a highly organized structure in the extracellular milieu, sometimes occurring in chains that link neighboring cells within a biofilm. OMVs may be a vehicle for mediating wolf pack activity by delivering hydrolytic enzymes and antibiotics aimed at killing prey microbes. Here, both the protein and small molecule cargo of the OMV and membrane fractions of M. xanthus were characterized and compared. Our analysis indicates a number of proteins that are OMV-specific or OMV-enriched, including several with putative hydrolytic function. Secondary metabolite profiling of OMVs identifies 16 molecules, many associated with antibiotic activities. Several hydrolytic enzyme homologs were identified, including the protein encoded by MXAN_3564 (mepA), an M36 protease homolog. Genetic disruption of mepA leads to a significant reduction in extracellular protease activity suggesting MepA is part of the long-predicted (yet to date undetermined) extracellular protease suite of M. xanthus.
doi:10.3389/fmicb.2014.00474
PMCID: PMC4158809  PMID: 25250022
predation; fruiting body; predatory rippling; predator-prey interactions; secondary metabolism and enzymes
3.  Chemosensory signaling controls motility and subcellular polarity in Myxococcus xanthus 
Current opinion in microbiology  2012;15(6):751-757.
Myxococcus xanthus is a model system for the study of dynamic protein localization and cell polarity in bacteria. M. xanthus cells are motile on solid surfaces enabled by two forms of gliding motility. Motility is controlled by the Che-like Frz pathway, which is essential for fruiting body formation and differentiation. The Frz signal is mediated by a GTPase/GAP protein pair that establishes cell polarity and directs the motility systems. Pilus driven motility at the leading pole of the cell requires dynamic localization of two ATPases and the coordinated production of EPS synthesis. Gliding motility requires dynamic movement of large protein complexes, but the mechanism by which this system generates propulsive force is still an active area of investigation.
doi:10.1016/j.mib.2012.10.005
PMCID: PMC4123438  PMID: 23142584
4.  AglZ regulates adventurous (A-) motility in Myxococcus xanthus through its interaction with the cytoplasmic receptor, FrzCD 
Molecular microbiology  2009;72(4):964-977.
Summary
Myxococcus xanthus moves by gliding motility powered by Type IV pili (S-motility) and distributed motor complexes (A-motility). The Frz chemosensory pathway controls reversals for both motility systems. However, it is unclear how the Frz pathway can communicate with these different systems. In this paper, we show that FrzCD, the Frz pathway receptor, interacts with AglZ, a protein associated with A-motility. Affinity chromatography and cross-linking experiments showed that the FrzCD-AglZ interaction occurs between the uncharacterized N-terminal region of FrzCD and the N-terminal pseudo-receiver domain of AglZ. Fluorescence microscopy showed AglZ-mCherry and FrzCD-GFP localized in clusters that occupy different positions in cells. To study the role of the Frz system in the regulation of A-motility, we constructed aglZ frzCD double mutants and aglZ frzCD pilA triple mutants. To our surprise, these mutants, predicted to show no A-motility (A−S+) or no motility at all (A−S−), respectively, showed restored A-motility. These results indicate that AglZ modulates a FrzCD activity that inhibits A-motility. We hypothesize that AglZ-FrzCD interactions are favored when cells are isolated and moving by A-motility and inhibited when S-motility predominates and A-motility is reduced.
doi:10.1111/j.1365-2958.2009.06697.x
PMCID: PMC4098657  PMID: 19400788
M. xanthus; A-motility; Frz pathway; clusters
5.  Evidence That Focal Adhesion Complexes Power Bacterial Gliding Motility 
Science (New York, N.Y.)  2007;315(5813):853-856.
The bacterium Myxococcus xanthus has two motility systems: S motility, which is powered by type IV pilus retraction, and A motility, which is powered by unknown mechanism(s). We found that A motility involved transient adhesion complexes that remained at fixed positions relative to the substratum as cells moved forward. Complexes assembled at leading cell poles and dispersed at the rear of the cells. When cells reversed direction, the A-motility clusters relocalized to the new leading poles together with S-motility proteins. The Frz chemosensory system coordinated the two motility systems. The dynamics of protein cluster localization suggest that intracellular motors and force transmission by dynamic focal adhesions can power bacterial motility.
doi:10.1126/science.1137223
PMCID: PMC4095873  PMID: 17289998
6.  Phosphorylation-dependent localization of the response regulator FrzZ signals cell reversals in Myxococcus xanthus 
Molecular microbiology  2013;88(4):740-753.
Summary
The life cycle of Myxococcus xanthus includes coordinated group movement and fruiting body formation, and requires directed motility and controlled cell reversals. Reversals are achieved by inverting cell polarity and re-organizing many motility proteins. The Frz chemosensory pathway regulates the frequency of cell reversals. While it has been established that phosphotransfer from the kinase FrzE to the response regulator FrzZ is required, it is unknown how phosphorylated FrzZ, the putative output of the pathway, targets the cell polarity axis. In this study, we used Phos-tag SDS-PAGE to determine the cellular level of phospho-FrzZ under different growth conditions and in Frz signaling mutants. We detected consistent FrzZ phosphorylation, albeit with a short half-life, in cells grown on plates, but not from liquid culture. The available pool of phospho-FrzZ correlated with reversal frequencies, with higher levels found in hyper-reversing mutants. Phosphorylation was not detected in hypo-reversing mutants. Fluorescence microscopy revealed that FrzZ is recruited to the leading cell pole upon phosphorylation and switches to the opposite pole during reversals. These results are consistent with the hypothesis that the Frz pathway modulates reversal frequency through a localized response regulator that targets cell polarity regulators at the leading cell pole.
doi:10.1111/mmi.12219
PMCID: PMC3674769  PMID: 23551551
7.  Functional Organization of a Multimodular Bacterial Chemosensory Apparatus 
PLoS Genetics  2014;10(3):e1004164.
Chemosensory systems (CSS) are complex regulatory pathways capable of perceiving external signals and translating them into different cellular behaviors such as motility and development. In the δ-proteobacterium Myxococcus xanthus, chemosensing allows groups of cells to orient themselves and aggregate into specialized multicellular biofilms termed fruiting bodies. M. xanthus contains eight predicted CSS and 21 chemoreceptors. In this work, we systematically deleted genes encoding components of each CSS and chemoreceptors and determined their effects on M. xanthus social behaviors. Then, to understand how the 21 chemoreceptors are distributed among the eight CSS, we examined their phylogenetic distribution, genomic organization and subcellular localization. We found that, in vivo, receptors belonging to the same phylogenetic group colocalize and interact with CSS components of the respective phylogenetic group. Finally, we identified a large chemosensory module formed by three interconnected CSS and multiple chemoreceptors and showed that complex behaviors such as cell group motility and biofilm formation require regulatory apparatus composed of multiple interconnected Che-like systems.
Author Summary
Myxococcus xanthus is a social bacterium that exhibits a complex life cycle including biofilm formation, microbial predation and the formation of multicellular fruiting bodies. Genomic analyses indicate that M. xanthus produces an unusual number of chemosensory proteins: eight chemosensory systems (CSS) and 21 chemoreceptors, 13 of which are orphans located outside operons. In this paper we used genetic, phylogenetic and cell biology techniques to analyze the organization of the chemoreceptors and their functions in the regulation of M. xanthus social behaviors. Results indicate the existence of one large and three small chemosensory modules that occupy different positions within cells. This organization is consistent with in vivo protein interaction assays. Our analyses revealed the presence of a complex network of regulators that might integrate different stimuli to modulate bacterial social behaviors. Such networks might be conserved in other bacterial species with a life cycle of similar complexity and whose genome carries multiple CSS encoding operons.
doi:10.1371/journal.pgen.1004164
PMCID: PMC3945109  PMID: 24603697
8.  Uncovering the Mystery of Gliding Motility in the Myxobacteria 
Annual Review of Genetics  2011;45:21-39.
Bacterial gliding motility is the smooth movement of cells on solid surfaces unaided by flagella or pili. Many diverse groups of bacteria exhibit gliding, but the mechanism of gliding motility has remained a mystery since it was first observed more than a century ago. Recent studies on the motility of Myxococcus xanthus, a soil myxobacterium, suggest a likely mechanism for gliding in this organism. About forty M. xanthus genes were shown to be involved in gliding motility, and some of their protein products were labeled and localized within cells. These studies suggest that gliding motility in M. xanthus involves large multiprotein structural complexes, regulatory proteins, and cytoskeletal filaments. In this review, we summarize recent experiments that provide the basis for this emerging view of M. xanthus motility. We also discuss alternative models for gliding.
doi:10.1146/annurev-genet-110410-132547
PMCID: PMC3397683  PMID: 21910630
Myxococcus xanthus; proton motive force; cytoskeleton; protein localization; model
9.  FrzS Regulates Social Motility in Myxococcus xanthus by Controlling Exopolysaccharide Production 
PLoS ONE  2011;6(8):e23920.
Myxococcus xanthus Social (S) motility occurs at high cell densities and is powered by the extension and retraction of Type IV pili which bind ligands normally found in matrix exopolysaccharides (EPS). Previous studies showed that FrzS, a protein required for S-motility, is organized in polar clusters that show pole-to-pole translocation as cells reverse their direction of movement. Since the leading cell pole is the site of both the major FrzS cluster and type IV pilus extension/retraction, it was suggested that FrzS might regulate S-motility by activating pili at the leading cell pole. Here, we show that FrzS regulates EPS production, rather than type IV pilus function. We found that the frzS phenotype is distinct from that of Type IV pilus mutants such as pilA and pilT, but indistinguishable from EPS mutants, such as epsZ. Indeed, frzS mutants can be rescued by the addition of purified EPS, 1% methylcellulose, or co-culturing with wildtype cells. Our data also indicate that the cell density requirement in S-motility is likely a function of the ability of cells to construct functional multicellular clusters surrounding an EPS core.
doi:10.1371/journal.pone.0023920
PMCID: PMC3158785  PMID: 21886839
10.  Gliding Motility Revisited: How Do the Myxobacteria Move without Flagella? 
Summary: In bacteria, motility is important for a wide variety of biological functions such as virulence, fruiting body formation, and biofilm formation. While most bacteria move by using specialized appendages, usually external or periplasmic flagella, some bacteria use other mechanisms for their movements that are less well characterized. These mechanisms do not always exhibit obvious motility structures. Myxococcus xanthus is a motile bacterium that does not produce flagella but glides slowly over solid surfaces. How M. xanthus moves has remained a puzzle that has challenged microbiologists for over 50 years. Fortunately, recent advances in the analysis of motility mutants, bioinformatics, and protein localization have revealed likely mechanisms for the two M. xanthus motility systems. These results are summarized in this review.
doi:10.1128/MMBR.00043-09
PMCID: PMC2884410  PMID: 20508248
11.  A Multi-protein Complex from Myxococcus xanthus Required for Bacterial Gliding Motility 
Molecular microbiology  2010;76(6):1539-1554.
Myxococcus xanthus moves by gliding motility powered by Type IV pili (S-motility) and a second motility system, A-motility, whose mechanism remains elusive despite the identification of ~40 A-motility genes. In this study, we used biochemistry and cell biology analyses to identify multi-protein complexes associated with A-motility. Previously, we showed that the N-terminal domain of FrzCD, the receptor for the frizzy chemosensory pathway, interacts with two A-motility proteins, AglZ and AgmU. Here we characterized AgmU, a protein that localized to both the periplasm and cytoplasm. On firm surfaces, AgmU-mCherry co-localized with AglZ as distributed clusters that remained fixed with respect to the substratum as cells moved forward. Cluster formation was favored by hard surfaces where A-motility is favored. In contrast, AgmU-mCherry clusters were not observed on soft agar surfaces or when cells were in large groups, conditions that favor S-motility. Using glutathione-S-transferase (GST) affinity chromatography, AgmU was found to interact either directly or indirectly with multiple A-motility proteins including AglZ, AglT, AgmK, AgmX, AglW and CglB. These proteins, important for the correct localization of AgmU and AglZ, appear to be organized as a motility complex, spanning the cytoplasm, inner membrane and the periplasm. Identification of this complex may be important for uncovering the mechanism of A-motility.
doi:10.1111/j.1365-2958.2010.07184.x
PMCID: PMC2908308  PMID: 20487265
M. xanthus; A-motility; AgmU clusters; surface hardness; protein complex
12.  Developments in Defining dif▿  
Journal of Bacteriology  2010;192(17):4264-4266.
doi:10.1128/JB.00700-10
PMCID: PMC2937369  PMID: 20601469
13.  In vitro communities derived from oral and gut microbial floras inhibit the growth of bacteria of foreign origins 
Microbial ecology  2010;60(3):665-676.
The gastrointestinal (GI) tract is home to trillions of microbes. Within the same GI tract substantial differences in the bacterial species that inhabit the oral cavity and intestinal tract have been noted. While the influence of host environments and nutritional availability in shaping different microbial communities is widely accepted, we hypothesize that the existing microbial flora also plays a role in selecting the bacterial species that are being integrated into the community. In this study, we used cultivable microbial communities isolated from different parts of the GI tract of mice (oral cavity and intestines) as a model system to examine this hypothesis. Microbes from these two areas were harvested and cultured using the same nutritional conditions, which led to two distinct microbial communities, each with about 20 different species as revealed by PCR-DGGE analysis. In vitro community competition assays showed that the two microbial floras exhibited antagonistic interactions towards each other. More interestingly, all the original isolates tested and their closely related species displayed striking community preferences: they persisted when introduced into the bacterial community of the same origin, while their viable count declined more than 3 orders of magnitude after 4 days of coincubation with the microbial flora of foreign origin. These results suggest that an existing microbial community might impose a selective pressure on incoming foreign bacterial species independent of host selection. The observed inter-flora interactions could contribute to the protective effect of established microbial communities against the integration of foreign bacteria to maintain the stability of the existing communities.
doi:10.1007/s00248-010-9711-9
PMCID: PMC2954289  PMID: 20625712
14.  Oral-derived bacterial flora defends its domain by recognizing and killing intruders---- a molecular analysis using Escherichia coli as a model intestinal bacterium 
Microbial ecology  2010;60(3):655-664.
Within the same human gastrointestinal (GI) tract, substantial differences in the bacterial species that inhabit oral cavity and intestinal tract have been noted. Previous research primarily attributed the differences to the influences of host environments and nutritional availabilities (“host habitat” effect). Our recent study indicated that, other than the host habitat effect, an existing microbial community could impose a selective pressure on incoming foreign bacterial species independent of host-mediated selection (“community selection” effect). In this study, we employed in vitro microbial floras representing microorganisms that inhabit the oral cavities and intestinal tract of mice in combination with Escherichia coli as a model intestinal bacterium and demonstrated that E. coli displays a striking community preference. It thrived when introduced into the intestinal microbial community, and survived poorly in the microbial flora of foreign origin (oral community). A more detailed examination of this phenomenon showed that the oral community produced oxygen free radicals in the presence of wild type E. coli while mutants deficient in lipopolysaccharides (LPS) did not trigger significant production of these cell damaging agents. Furthermore, mutants of E. coli defective in the oxidative stress response experienced a more drastic reduction in viability when co-cultivated with the oral flora, while the exogenous addition of the anti-oxidant vitamin C was able to rescue it. We concluded that the oral-derived microbial community senses the E. coli LPS and kills the bacterium with oxygen free radicals. This study reveals a new mechanism of community invasion resistance employed by established microflora to defend their domains.
doi:10.1007/s00248-010-9708-4
PMCID: PMC2954290  PMID: 20625713
15.  In Vitro Communities Derived from Oral and Gut Microbial Floras Inhibit the Growth of Bacteria of Foreign Origins 
Microbial Ecology  2010;60(3):665-676.
The gastrointestinal (GI) tract is home to trillions of microbes. Within the same GI tract, substantial differences in the bacterial species that inhabit the oral cavity and intestinal tract have been noted. While the influence of host environments and nutritional availability in shaping different microbial communities is widely accepted, we hypothesize that the existing microbial flora also plays a role in selecting the bacterial species that are being integrated into the community. In this study, we used cultivable microbial communities isolated from different parts of the GI tract of mice (oral cavity and intestines) as a model system to examine this hypothesis. Microbes from these two areas were harvested and cultured using the same nutritional conditions, which led to two distinct microbial communities, each with about 20 different species as revealed by PCR-based denaturing gradient gel electrophoresis analysis. In vitro community competition assays showed that the two microbial floras exhibited antagonistic interactions toward each other. More interestingly, all the original isolates tested and their closely related species displayed striking community preferences: They persisted when introduced into the bacterial community of the same origin, while their viable count declined more than three orders of magnitude after 4 days of coincubation with the microbial flora of foreign origin. These results suggest that an existing microbial community might impose a selective pressure on incoming foreign bacterial species independent of host selection. The observed inter-flora interactions could contribute to the protective effect of established microbial communities against the integration of foreign bacteria to maintain the stability of the existing communities.
Electronic supplementary material
The online version of this article (doi:10.1007/s00248-010-9711-9) contains supplementary material, which is available to authorized users.
doi:10.1007/s00248-010-9711-9
PMCID: PMC2954289  PMID: 20625712
16.  Oral-Derived Bacterial Flora Defends Its Domain by Recognizing and Killing Intruders—A Molecular Analysis Using Escherichia coli as a Model Intestinal Bacterium 
Microbial Ecology  2010;60(3):655-664.
Within the same human gastrointestinal tract, substantial differences in the bacterial species that inhabit oral cavity and intestinal tract have been noted. Previous research primarily attributed the differences to the influences of host environments and nutritional availabilities (“host habitat” effect). Our recent study indicated that, other than the host habitat effect, an existing microbial community could impose a selective pressure on incoming foreign bacterial species independent of host-mediated selection (“community selection” effect). In this study, we employed in vitro microbial floras representing microorganisms that inhabit the oral cavities and intestinal tract of mice in combination with Escherichia coli as a model intestinal bacterium and demonstrated that E. coli displays a striking community preference. It thrived when introduced into the intestinal microbial community and survived poorly in the microbial flora of foreign origin (oral community). A more detailed examination of this phenomenon showed that the oral community produced oxygen-free radicals in the presence of wild-type E. coli while mutants deficient in lipopolysaccharides (LPS) did not trigger significant production of these cell-damaging agents. Furthermore, mutants of E. coli defective in the oxidative stress response experienced a more drastic reduction in viability when cocultivated with the oral flora, while the exogenous addition of the antioxidant vitamin C was able to rescue it. We concluded that the oral-derived microbial community senses the E. coli LPS and kills the bacterium with oxygen-free radicals. This study reveals a new mechanism of community invasion resistance employed by established microflora to defend their domains.
Electronic supplementary material
The online version of this article (doi:10.1007/s00248-010-9708-4) contains supplementary material, which is available to authorized users.
doi:10.1007/s00248-010-9708-4
PMCID: PMC2954290  PMID: 20625713
17.  The receiver domain of FrzE, a CheA-CheY fusion protein, regulates the CheA histidine kinase activity and downstream signaling to the A- and S-motility systems of Myxococcus xanthus 
Molecular microbiology  2008;68(5):1328-1339.
The Frz chemosensory system is a two-component signal transduction pathway that controls cell reversals and directional movements for the two motility systems in Myxococcus xanthus. To trigger cell reversals, FrzE, a hybrid CheA-CheY fusion protein, autophosphorylates the kinase domain at His-49 and phosphoryl groups are transferred to aspartate residues (Asp-52 and Asp-220) in the two receiver domains of FrzZ, a dual CheY-like protein that serves as the pathway output. The role of the receiver domain of FrzE was unknown. In this paper, we characterize the FrzE protein in vitro and show that the receiver domain of FrzE negatively regulates the autophosphorylation activity of the kinase domain of FrzE. Unexpectedly, it does not appear to play a direct role in phospho-relay as in most other histidine kinase-receiver domain hybrid systems. The regulatory role of the FrzE receiver domain suggests that it may interact with or be phosphorylated by an unknown protein. We also show the dynamics of motility system specific marker proteins in FrzE mutants as cells move forward and reverse. Our studies indicate that the two motility systems are functionally coordinated and that any system specific branching to the pathway most likely occurs downstream of FrzE.
doi:10.1111/j.1365-2958.2008.06238.x
PMCID: PMC2830897  PMID: 18430134
18.  Site-specific receptor methylation of FrzCD in Myxococcus xanthus is controlled by a TPR containing regulatory domain of the FrzF methyltransferase 
Molecular microbiology  2008;69(3):724-735.
Summary
Myxococcus xanthus is a gliding bacterium with a complex life cycle that includes swarming, predation, and fruiting body formation. Directed movements in M. xanthus are regulated by the Frz chemosensory system, which controls cell reversals. The Frz pathway requires the activity of FrzCD, a cytoplasmic methyl accepting chemotaxis protein (MCP), and FrzF, a methyltransferase (CheR) containing an additional domain with three tetra trico-peptide repeats (TPRs). To investigate the role of the TPRs in FrzCD methylation, we used full-length FrzF and FrzF lacking its TPRs (FrzFCheR) to methylate FrzCD in vitro. FrzF methylated FrzCD on a single residue, E182, while FrzFCheR methylated FrzCD on three residues, E168, E175, and E182, indicating that the TPRs regulate site-specific methylation. E168 and E182 were predicted consensus methylation sites, but E175 is methylated on an HE pair. To determine the roles of these sites in vivo, we substituted each methylatable glutamate with either an aspartate or an alanine residue and determined the impact of the point mutants on single cell reversals, swarming and fruiting body formation. Single, double, and triple methylation site mutants revealed that each site played a unique role in M. xanthus behavior and that the pattern of receptor methylation determined receptor activity. This work also shows that methylation can both activate and inactivate the receptor.
doi:10.1111/j.1365-2958.2008.06323.x
PMCID: PMC2535941  PMID: 18554333
19.  Polarity of motility systems in Myxococcus xanthus 
Current opinion in microbiology  2007;10(6):624-629.
Myxococcus xanthus is a gliding bacterium that contains two motility systems: S-motility, powered by polar type IV pili, and A-motility, powered by uncharacterized motors and adhesion complexes. The localization and coordination of the two motility engines is essential for directed motility as cells move forward and reverse. During cell reversals, the polarity and localization of motility proteins are rapidly inverted, rendering this system a fascinating example of dynamic protein localization.
doi:10.1016/j.mib.2007.09.012
PMCID: PMC2170899  PMID: 17981496
20.  EspA, an Orphan Hybrid Histidine Protein Kinase, Regulates the Timing of Expression of Key Developmental Proteins of Myxococcus xanthus▿  
Journal of Bacteriology  2008;190(13):4416-4426.
Myxococcus xanthus undergoes a complex starvation-induced developmental program that results in cells forming multicellular fruiting bodies by aggregating into mounds and then differentiating into spores. This developmental program requires at least 72 h and is mediated by a temporal cascade of gene regulators in response to intra- and extracellular signals. espA mutants, encoding an orphan hybrid histidine kinase, alter the timing of this developmental program, greatly accelerating developmental progression. Here, we characterized EspA and demonstrated that it autophosphorylates in vitro on the conserved histidine residue and then transfers the phosphoryl group to the conserved aspartate residue in the associated receiver domain. The conserved histidine and aspartate residues were both required for EspA function in vivo. Analysis of developmental gene expression and protein accumulation in espA mutants indicated that the expression of the A-signal-dependent spi gene was not affected but that the MrpC transcriptional regulator accumulated earlier, resulting in earlier expression of its target, the FruA transcriptional regulator. Early expression of FruA correlated with acceleration of both the aggregation and sporulation branches of the developmental program, as monitored by early methylation of the FrzCD chemosensory receptor and early expression of the sporulation-specific dev and Mxan_3227 (Ω7536) genes. These results show that EspA plays a key role in the timing of expression of genes necessary for progression of cells through the developmental program.
doi:10.1128/JB.00265-08
PMCID: PMC2446797  PMID: 18390653
21.  Site-specific receptor methylation of FrzCD in Myxococcus xanthus is controlled by a tetra-trico peptide repeat (TPR) containing regulatory domain of the FrzF methyltransferase 
Molecular Microbiology  2008;69(3):724-735.
Myxococcus xanthus is a gliding bacterium with a complex life cycle that includes swarming, predation and fruiting body formation. Directed movements in M. xanthus are regulated by the Frz chemosensory system, which controls cell reversals. The Frz pathway requires the activity of FrzCD, a cytoplasmic methyl-accepting chemotaxis protein, and FrzF, a methyltransferase (CheR) containing an additional domain with three tetra trico-peptide repeats (TPRs). To investigate the role of the TPRs in FrzCD methylation, we used full-length FrzF and FrzF lacking its TPRs (FrzFCheR) to methylate FrzCD in vitro. FrzF methylated FrzCD on a single residue, E182, while FrzFCheR methylated FrzCD on three residues, E168, E175 and E182, indicating that the TPRs regulate site-specific methylation. E168 and E182 were predicted consensus methylation sites, but E175 is methylated on an HE pair. To determine the roles of these sites in vivo, we substituted each methylatable glutamate with either an aspartate or an alanine residue and determined the impact of the point mutants on single cell reversals, swarming and fruiting body formation. Single, double and triple methylation site mutants revealed that each site played a unique role in M. xanthus behaviour and that the pattern of receptor methylation determined receptor activity. This work also shows that methylation can both activate and inactivate the receptor.
doi:10.1111/j.1365-2958.2008.06323.x
PMCID: PMC2535941  PMID: 18554333
22.  The Motors Powering A-Motility in Myxococcus xanthus Are Distributed along the Cell Body▿  
Journal of Bacteriology  2007;189(21):7920-7921.
Two models have been proposed to explain the adventurous gliding motility of Myxococcus xanthus: (i) polar secretion of slime and (ii) an unknown motor that uses cell surface adhesion complexes that form periodic attachments along the cell length. Gliding movements of the leading poles of cephalexin-treated filamentous cells were observed but not equivalent movements of the lagging poles. This demonstrates that the adventurous-motility motors are not confined to the rear of the cell.
doi:10.1128/JB.00923-07
PMCID: PMC2168729  PMID: 17704221
23.  Aggregation during Fruiting Body Formation in Myxococcus xanthus Is Driven by Reducing Cell Movement▿ †  
Journal of Bacteriology  2006;189(2):611-619.
When starved, Myxococcus xanthus cells assemble themselves into aggregates of about 105 cells that grow into complex structures called fruiting bodies, where they later sporulate. Here we present new observations on the velocities of the cells, their orientations, and reversal rates during the early stages of fruiting body formation. Most strikingly, we find that during aggregation, cell velocities slow dramatically and cells orient themselves in parallel inside the aggregates, while later cell orientations are circumferential to the periphery. The slowing of cell velocity, rather than changes in reversal frequency, can account for the accumulation of cells into aggregates. These observations are mimicked by a continuous agent-based computational model that reproduces the early stages of fruiting body formation. We also show, both experimentally and computationally, how changes in reversal frequency controlled by the Frz system mutants affect the shape of these early fruiting bodies.
doi:10.1128/JB.01206-06
PMCID: PMC1797407  PMID: 17098901
24.  An atypical receiver domain controls the dynamic polar localization of the Myxococcus xanthus social motility protein FrzS 
Molecular Microbiology  2007;65(2):319-332.
The Myxococcus xanthus FrzS protein transits from pole-to-pole within the cell, accumulating at the pole that defines the direction of movement in social (S) motility. Here we show using atomic-resolution crystallography and NMR that the FrzS receiver domain (RD) displays the conserved switch Tyr102 in an unusual conformation, lacks the conserved Asp phosphorylation site, and fails to bind Mg2+ or the phosphoryl analogue, Mg2+·BeF3. Mutation of Asp55, closest to the canonical site of RD phosphorylation, showed no motility phenotype in vivo, demonstrating that phosphorylation at this site is not necessary for domain function. In contrast, the Tyr102Ala and His92Phe substitutions on the canonical output face of the FrzS RD abolished S-motility in vivo. Single-cell fluorescence microscopy measurements revealed a striking mislocalization of these mutant FrzS proteins to the trailing cell pole in vivo. The crystal structures of the mutants suggested that the observed conformation of Tyr102 in the wild-type FrzS RD is not sufficient for function. These results support the model that FrzS contains a novel ‘pseudo-receiver domain’ whose function requires recognition of the RD output face but not Asp phosphorylation.
doi:10.1111/j.1365-2958.2007.05785.x
PMCID: PMC1974792  PMID: 17573816
25.  Four Unusual Two-Component Signal Transduction Homologs, RedC to RedF, Are Necessary for Timely Development in Myxococcus xanthus 
Journal of Bacteriology  2005;187(23):8191-8195.
We identified a cluster of four two-component signal transduction genes that are necessary for proper progression of Myxococcus xanthus through development. redC to redF mutants developed and sporulated early, resulting in small, numerous, and disorganized fruiting bodies. Yeast two-hybrid analyses suggest that RedCDEF act in a single signaling pathway. The previously identified espA gene displays a phenotype similar to that of redCDEF. However, combined mutants defective in espA redCDEF exhibited a striking additive developmental phenotype, suggesting that EspA and RedC to RedF play independent roles in controlling developmental progression.
doi:10.1128/JB.187.23.8191-8195.2005
PMCID: PMC1291262  PMID: 16291693

Results 1-25 (35)